1. Field
The disclosure of the present application relates to a diaphragm and a speaker device provided with the same.
2. Description of Related Art
The conventional speaker device includes a drive system equipped mainly with a magnetic circuit and a voice coil, a diaphragm for vibrating air, and a support system for supporting the diaphragm. A cone-type speaker device (for the bass reproduction, full-range reproduction, etc.) and a dome-type speaker (for the treble reproduction) are known generally as a speaker device with the above-described configuration.
JP 2005-123779 A discloses a technique for improving fluctuations in a sound pressure frequency response, especially in a treble part, by providing thick parts having different thicknesses at several locations on a cone-type diaphragm.
JP 60 (1985)-47597 A discloses a technique of making a cone-type diaphragm gradually thinner from the center to the outer circumferential side for reducing the weight of the diaphragm.
Thus, the conventional speaker device is able to reproduce music with good sound quality by improving the diaphragm.
However, as described in Non-Patent Document 1 (“Speaker System” written by Takeo Yamamoto, Radio Technology, published in 1977), when vibrations having frequencies from the midrange (about 2 kHz) to the treble (about 20 kHz) are applied on a common diaphragm for a cone-type speaker device, separate vibrations sometimes occur, which worsens the quality of output sounds. Specifically, since the strength of the conventional diaphragm on the outer circumferential side is not sufficient, separate vibrations in a circumferential direction occur on the outer circumferential side when midrange signals are input. Further, since the strength of the conventional diaphragm on the inner circumferential side is not sufficient, separate vibrations in the circumferential direction occur on the inner circumferential side when treble signals are input. Moreover, in specific frequencies in the midrange and the treble, separate vibrations in a radiation direction sometimes occur. Because of these influences, in the conventional speaker device, there has been a problem that large peaks and dips occur in the sound pressure frequency response and fluctuations occur in sounds. Note here that “separate vibration” refers to the motion by which the diaphragm vibrates while bending.
Further, the thick parts of the diaphragm disclosed in JP 2005-123779 A have a uniform length, and parts other than the thick parts are made gradually thinner from the outer circumferential side to the inner circumferential side. With this configuration, although fluctuations in the sound pressure frequency response are reduced, the decrease in the strength of the diaphragm on the inner circumferential side reduces the sound pressure in the treble. Therefore, such a configuration is not suitable for enlarging a reproduction band in the treble.